The present invention relates to a method and apparatus for manipulating the composition of a fluid or fluids, and more particularly, to a method and apparatus for producing fluid gradients.
Delivery of fluids for industrial, chemical and biological applications has evolved to a point where extremely small, or very large, quantities of fluid can be accurately delivered using a variety of pumping and pipetting techniques. In addition, techniques have been developed for eroding surfaces and for applying chemicals to surfaces in very precise quantities and at specific locations. These techniques may be used to apply solutions and suspensions accurately and evenly over a surface to provide consistent surface chemical densities. However, applications may exist where it is not desirable to introduce or deposit solutions or chemicals evenly, but rather as a gradient where the density of an applied material is greater at one part of a surface than it is at another part of the surface.
Traditionally, linear concentration gradients exhibiting a variation in concentration in relation to distance may be formed by allowing solutes to diffuse from a point of high concentration into a material containing the substance at low concentration. After the substance has been allowed to diffuse for a period of time, a concentration gradient may develop extending away from the point source. The fluid may be sampled at various distances from the point source and progressively lower concentrations will generally be detected as the distance from the point source increases. Unfortunately, because materials in solution continue to diffuse to areas of lesser concentration, the concentration of the substance at any one point changes with time, as does the gradient between any two points. It is therefore difficult to proceed with experiments or processes that require a stable gradient. This problem is compounded when steep gradients are required, as steep gradients generally may decay faster than those that are less sloped.
Gradients on surfaces have been produced by methods using self-assembled monolayers (SAMs) including cross-diffusion, photo-immobilization and electrochemical desorption. However, the types of gradients profiles on surfaces that can be produced, the substances that can be used, and the size of the gradients are all limited.
In addition, known fluid gradients may be limited to linear gradients in which concentration decreases or increases by a constant amount over distance. At times, it may be useful to employ gradient that do not increase or decrease linearly, but rather increase, for example, as a squared, cubed or logarithmic function. However, known point source and linear source diffusion techniques are not known to be capable of producing gradients that exhibit these profiles.
In one aspect, the invention provides an apparatus comprising a first generation having at least two first generation channels, a common channel providing communication between each of at least two of the first generation channels, and a second generation comprising at least three second generation channels, each of the second generation channels having a first end and a second end with the first end of each being in communication with the common channel.
In another aspect, the invention provides for a method of forming a gradient comprising passing a fluid through a first channel, passing a second fluid through a second channel, joining the first fluid and the second fluid in a common channel, passing fluid from the common channel into at least three additional channels and recombining the fluid from the three additional channels into a single channel under conditions of substantially laminar flow.
In another aspect, the invention provides for a fluid stream comprising a first substance that varies in concentration in a direction that is substantially perpendicular to the direction of the flow of the fluid, and includes a second substance that varies in concentration in a direction substantially perpendicular to the direction of the flow of the fluid, and has a concentration gradient of the first substance that is of a different profile than a concentration gradient of the second substance.
In another aspect, the invention provides for an nth order polynomial concentration gradient where n is greater than or equal to 2.
In another aspect, the invention provides for a surface comprising a first chemical or biochemical gradient disposed on a portion of the surface, a second chemical or biochemical gradient disposed on the portion of the surface and a third chemical or biochemical gradient disposed on a portion of the surface, wherein each of the gradients is different.
In another aspect, the invention provides for a method of treating a surface comprising passing a fluid along a portion of a surface under conditions of substantially laminar flow wherein the fluid comprises a concentration gradient of at least one substance, the concentration gradient being substantially perpendicular to the direction of flow and substantially continuous across a fluid, and treating differentially a plurality of sections of the portion of the surface exposed to different concentrations of the substance.
In another aspect, the invention provides for a method of diluting a fluid comprising feeding a high concentration fluid to a first inlet, feeding a low concentration fluid to a second inlet, passing the fluid from the first inlet and the fluid from the second inlet into a first generation channel, splitting the fluid in the common channel into at least three second generation channels, recombining the fluids from the at least three second generation channels into a second generation common channel, splitting the fluid in the second generation common channel into a plurality of third generation channels, and collecting fluid from at least one of the plurality of third generation channels.
In another aspect, the invention provides for a method of producing a fluid exhibiting two different concentration gradient profiles comprising combining at least a first starting fluid with a second starting fluid to form a combined stream, the first starting fluid comprising a first substance that is substantially absent from the second fluid, dividing the combined stream into a series of second stage streams, and joining at least two of the second stage streams to form a composite stream wherein the composite stream exhibits a different concentration gradient profile for the first substance and a second substance.
In another aspect, the invention provides for a method of producing a series of solutions comprising contacting a concentrated solution of a substance and a less concentrated solution of a substance to form a combined fluid and separating the combined fluid, without using a membrane, into a plurality of separate streams wherein at least one of the separate streams comprises a substance at a concentration that is substantially different than the concentration of the substance in another of the separate streams.
Other advantages, novel features, and objects of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings, which are schematic and which are not intended to be drawn to scale. In the figures, each identical or nearly identical component that is illustrated in various figures is represented by a single numeral. For purposes of clarity, not every component is labeled in every figure, nor is every component of each embodiment of the invention shown where illustration is not necessary to allow those of ordinary skill in the art to understand the invention.